choosing a pm motor + reversing motor direction


Thread Starter


i will be applying bang-bang control to a vehicle in a project. so i will choose a pm motor and reverse its direction at specific instants that are known beforehand. how can tell the system at what time to reverse direction? how can i reverse the direction of the motor? i dont know what driver to choose - along with using drivers:((
thanks in advance for your comments...

Steve Myres, PE

PMDC motors direction is dependent on their polarity, so you can reverse the direction by using a relay arrangement to reverse the leadwire connections. This can even be done with a single two pole relay. I wouldnt do this to a moving load with high inertia. For that there are at least two approaches.

You can decelerate the load with a braking resistor when you need to stop. Disconnect the motor from the controller and shunt the motor leads through a low value, high power resistor. I have used a 5 ohm, 100-200 watt resistor for a 1-2hp motor. The lower the resistance, the quicker the stop, and the larger the armature wires and power rating of the resistor will need to be. Once the load is stopped, you can reverse the motor connections, disconnect the resistor, and reconnect power to go the other way.

PMDC motors are frequently used with "four-quadrant regenerative drives". This would be the more elegant solution for your application. "Four-quadrant" means that the drive can apply torque in either direction while moving in either direction, that it can both motor and brake or "regenerate" in either forward or reverse motion. These drives usually have potentiometer input for speed control, and the input can range from full forward to full reverse. You would put your directional logic in the pot wiring, and be switching only very low power. The drive would take care of decelerating the load within the capabilities of the motor and the drive, and would then reverse automatically.

Drives like this are manufactured by KB Electronics, Minarik Electric, Extron, and others.

Rakesh Chandra Prajapati

generally for the small size system we can use 6vdc, 12vdc, 24vdc PMDC motor. for the control of direction of the motor we can use H-bridge. The choice of the switching transistor depends on the power of motor and the rate of switching! alternative sides transistors should be switched for the control of direction(reversing the direction of motor). one of the advantage of using H-bridge for control is that the speeh of the pmdc motor can also be contoled just by PWM method feed to the base of the bridge transistors!